Study and compare the origin and progressive enlargement of the "giant cells" that initiate and lead to macrocyst formation in homothallic strains (e.g. Dictyostelium mucoroides, strain #DM-7) and those that arise from the fusion of cells of opposite mating types in paired cultures of compatible strains in Dictyostelium discoideum (e.g., WS-10 (A1) plus WS-582 (A2)). Attempt to determine why cells of opposite mating type will form macrocysts when grown separately for 24 hrs and then brought together but will not do so when similarly grown for 48 hrs and then intermixed. Use time-lapse photography to follow macrocyst development from the origin of the giant cell (via fusion of myxamoebae of opposite mating types) to the completed ingestion of the surrounding cells and the deposition of the rigid delimiting cellulose wall. Investigate conditions favoring the formation and maturation of macrocysts by compatible mating types of D. rosarium. With such in hand determine optimal condition for cyst germination, leading to the possible use of such cysts in genetic studies. Complete our study of The Acrasea, modifying and enlarging the prescription of a few genera and species long recorded but still little known, and describing some new genera and species as our comparative studies dictate. BIBLIOGRAPHIC REFERENCE: Erodos, G.W., K.B. Raper and Linda K. Vogen. 1975. Sexuality in the cellular slime mold Dictyostelium giganteum. Proc. Nat. Acad. Sci. 72: 970-973.